The evolution of plasticity in brain morphology following colonization of an ecologically divergent habitat in Trinidadian guppies

Natural environments are constantly changing. To survive, organisms will
either need to rapidly adapt to new conditions or colonize new habitats.
Colonization has been hypothesized to select for increased plasticity as
well as increased brain size, though empirical tests of these effects have
proven difficult to evaluate. In particular, the degree to which
plasticity of brain morphology can evolve, and its subsequent ecological
consequences have rarely been explored. Trinidadian guppies (Poecilia
reticulata) are known for their repeated adaptation to ancestral
high-predation (HP) and derived low-predation (LP) environments. We used
this system to examine the evolution and plasticity of brain morphology.
We exposed second-generation offspring of individuals collected from HP
and LP sites to two different kinds of environmental treatments: predation
cues and conspecific social environment. We found that guppies descended
from a colonized LP habitat showed greater plasticity in brain morphology
than descendants of their ancestral HP population, supporting the
hypothesis that plasticity of brain morphology may increase fitness after
colonization of a novel habitat. Additionally, we show sexual dimorphism
in brain morphology plasticity. Overall, these results suggest the
evolution of brain morphology plasticity as an important mechanism that
allows for ecological diversification and colonization of novel habitats.